[Problems concerning standardization and quality assurance in DNA cytometry].

Rat liver imprints were treated with five different fixation techniques. Chicken erythrocytes stored over an extended period in the refrigerator were dropped on each slide before Feulgen staining. By means of an image analysis system chicken erythrocytes, rat leukocytes and hepatocytes were measured and the integrated optical density (IOD) was calculated for each nucleus. The coefficient of variation (CV) of IOD was about 15% for chicken erythrocytes. Leukocytes showed a CV of up to 10%. The CV was lower for hepatocytes than for leukocytes, and lowest for air-dried hepatocytes. The standard error of the mean (SEM) did not show remarkable differences between the fixation groups. For hepatocytes it was in general less than 1% of the respective mean value. The hepatocytes showed a linear staining except the wet formalin-fixed cells. This holds also for the wet formalin fixed leukocytes which showed only 85% of the IOD of 2c hepatocytes. The ratios of erythrocytes to 2c hepatocytes varied between 0.33 and 0.35. The IOD ratios of standard cells to 2c hepatocytes from single specimens showed remarkable differences from the above mentioned ratios of the pooled slides of a fixation group. The use of external standard cells was proved to be problematic, especially because of their variation in staining intensity independent of the staining intensity of hepatocytes.